In a broad sense, the concept of geothermal energy can also be extended to the study of other planets. Its principles are exploited at the technological level in the production of electricity and in cogeneration through geothermal power plants from associated geothermal energy.
In conclusion, geothermal is the relationship between Earth and the heat generated by it. On the other hand, there is geothermal energy, which is a related but different concept. Geothermal energy is the use of these natural conditions to take advantage of this thermal energy. The harnessed energy can be in the form of heat or in the form of electricity. In any case, it is a renewable energy source since the thermal resources of the Earth's interior are practically inexhaustible.
The origin of terrestrial heat from geothermal energy
The heat from the Earth's core was originally generated during the accretion of the developed planet thanks to the gravitational pull force. Later, heat continued to be generated thanks to the natural processes of nuclear fission of elements such as uranium, thorium and potassium.
Terrestrial heat is transferred from the interior to the Earth's surface through the Earth's mantle by convection produced by the movement of magma or deep water. This is the origin of most phenomena such as volcanic eruptions, and other associated geothermal phenomena, and thus evident on the surface of the earth, such as hot springs, geysers, and fumaroles.
This natural heat can be exploited for energy, specifically called geothermal energy. The term geothermal is often used to precisely indicate the exploitation of geothermal energy.
The heat flux from inside the Earth is only 1 / 20,000 of the heat that the Earth receives from the sun.
What is the thermal gradient?
Depending on the heat flux and thermal conductivity, which varies according to the type of soil or rock, a different thermal gradient is observed (temperature variation as a function of depth).
This gradient can vary from 1 ° C every 30 m from the surface part of the earth's crust to 1 ° C every 10 - 15 m from the seabed in the vicinity of the oceanic mountain ranges. The geothermal gradient in turn is strongly influenced by the circulation of internal terrestrial fluids.
Measurement of temperature and thermal gradient
The measurement is carried out with the appropriate instruments that are dropped into the geothermal wells. Accurate temperature measurement is complex and is disturbed by heat from drilling and by the presence of liquids (water, moisture, air) that may be present in the soil.
Accurate temperature measurement is the precision that it is a function of the machinery used and the purpose of the instrument type investigation.
Instruments for measuring temperature in geothermal wells
Thermometers used in geothermal investigations must have two important characteristics:
- Speed, therefore, must quickly reach thermal equilibrium. To have speed, therefore, these thermometers must have low thermal inertia.
- Reading should be possible when standing outside the well.
The thermometers used can therefore be distinguished in:
- Thermocouples (3/100 degree error)
- Resistance thermometers (1/100 degree error)
- Oscillators (error less than 1/1000 degrees)
What geothermal resources does the Earth have?
Earth's internal heat energy flows to the surface by conduction at a rate of 44.2 terawatts (TW), and is replenished by radioactive decay of minerals at a rate of 30 TW.
These amounts of energy are more than double humanity's current energy consumption from all primary sources, but most of this energy flow is not recoverable.
In addition to internal heat fluxes, the top layer of the surface at a depth of 10 meters is heated by solar energy during the summer and releases that energy and cools down in the winter.
What is an improved geothermal system?
An improved geothermal system (EGS) generates geothermal electricity without the need for natural convective hydrothermal resources.
Until recently, geothermal energy systems have only exploited resources where natural heat, water, and rock permeability are sufficient to allow energy extraction. However, by far most of the geothermal energy available to conventional techniques is in dry, impermeable rock.
EGS technologies enhance and / or create geothermal resources in this hot dry rock (HDR) through 'hydraulic stimulation'.